Parallax is a Mind Fuck,which is something many are quick to equate to "focus"...yet ain't.
Next time you go to shoot,simply do the Stevie Wonder Check and with a WELL rested rifle,gawk through the scope and move your head around with a full field of view. The reticle will move and that is parallax.
If one is shooting comfortably from a bench or similar and can mount the platform consistently,parallax can border closer to moot. Reality is,very few shoot in sucha' manner and as Utility Killing goes,it do very much play a role. As distance increases,so do the effects.
Had a buddy I work with call a coupla R&R's ago,scratching his head and motherfucking a sound rifle(Kali Kid Kustom),that was/is STUPID accurate,but "fell apart" at 700yds and out. I laughed and said "You are parallax fucking yourself",as he was driving a FFP 3-15x MQ with parallax adjustment. He tried to argue it and I asked if he was close to his rifle and he said "yes",as he was home. I told him to set it up static,looking out at a like distance and to Stevie Wonder,during the phone call. He goes "what in THE fuck?!?" and I re-laughed. There's not a better way to detect same and the Mind fuck is REAL,when you place crosshairs in a place the boolit don't fly to,due parallax.
Thus the affinity to scribe a parallax setting,with a platform's zero,as it is intuitive to KNOW you'll wanna correct either side of same,if/when opportunity allows.
Go do same and report back.
Toldjaso......................(grin)